With a wireless device including a layer 2 switch, the wireless section may be configured to be redundant. Redundancy with the wireless device including the layer 2 switch is generally made by IEEE 802.3 ad (a link aggregation). Such a redundant configuration is made in order to achieve load distribution (load balancing) or to improve fault tolerance.
With such a wireless device, switchover of a wireless port (a card-shaped device that carries out wireless communication) may take place in order to address an occurrence of a fault in the wireless port, replacement of the wireless port, a change in the wireless environment and the like. With the wireless device, when switchover of the wireless port takes place with the wireless section being configured to be redundant, a flush process (a clear process) of an FDB (Forward DataBase) learned by the layer 2 switch occurs. This flush process of the FDB causes flooding of frames. That is, unnecessary frame transfer is performed to disadvantageously increase the traffic. Further, missing (losses) of frames will be invited until communication is started with the wireless port newly switched to.
When the link aggregation is realized with the wireless device including the layer 2 switch, a wireless line termination unit (a card-shaped device that carries out wireless communication) that communicates via a wireless line exerts buffer control such as a transmission allocation and a transmission duplexing process. Further, the wireless line termination unit performs the ACT (active system)/SBY (standby system) management by software. For realizing these functions, it takes time for the wireless line termination unit to carry out the switchover process of the wireless port.
In the following, a description will be given of the technique relating to the aforementioned problem.
Patent Literature 1 discloses a data transfer method according to which all the main lines in a redundancy configuration can be switched. Patent Literature 1 discloses a redundant configuration in which a virtual path is generated by a plurality of main lines and one or more protection lines. Using the virtual path, transmission and reception of frames are performed.
Patent Literature 2 discloses a transfer system in which a link aggregation scheme is applied to a plurality of lines. With this system, a special frame referred to as the MRL (Multi-Radio-Line) frame is used for realizing the link aggregation.
Patent Literature 3 discloses a technique for performing the line switching between two lines while maintaining the traffic using layer 2 switches. Note that Patent Literature 3 is silent about the configuration in which redundancy is made in order to achieve the load distribution in the wireless section (an N+0 configuration).